1. Field of the Invention
The present invention relates to a technique to perform a gradation conversion process to an image so as to output the image and observe the output image.
2. Related Background Art
Conventionally, for example, in a personal computer in which a printer driver has been installed, when an image displayed on a monitor is output and printed by a printer, it is necessary for a user to adjust brightness of the image to be displayed (called a target image hereinafter) in a printed material (i.e., an output image) output by the printer. In order to do so, the user has to set automatic setting for the printer driver to automatically perform the brightness adjustment of the target image, set desired setting on adjustment setting items displayed on the personal computer to manually perform the brightness adjustment of the target image, or select an output gamma value.
Thus, on the basis of the automatic setting, the user's manual setting, or the selected output gamma value, the printer driver obtains a print density of the image in the printer corresponding to brightness of the image on the monitor, and calculates a gradation correction curve from the obtained print density. Then, the printer driver corrects the target image on the basis of the calculated gradation correction curve, whereby the brightness of the target image in the print output (i.e., image output) by the printer is adjusted.
On one hand, it has been conventionally known that sight of an image when observing the result (i.e., a printed material) output and printed by the printer is highly influenced by its observation environment. Particularly, with respect to the contrast and the brightness of the image, a human's visual characteristic changes in three environments (1) to (3) as follows. That is, the human's visual characteristic changes in (1) a pitch-dark state in such a case where a viewer observes a slide image or a projector image, (2) a darkish state in such a case where a viewer observes an OHP (overhead projector) sheet, and (3) a bright state or a light state which is known as an ordinary observation environment.
For example, even if there are two printed materials on which the images having the same gradation characteristic have been respectively output and printed, the contrast of the image on the printed material which is observed when the observation environment is the pitch-dark state is viewed as if it is lower than that of the image on the printed material which is observed when the observation environment is the bright state. Moreover, when the observation environment is the darkish state, it is said that a visual characteristic which is intermediate between two visual characteristics as above appears.
However, a conventional apparatus or system which performs such a gradation correction process (i.e., a gradation conversion process) is structured to set a gradation correction curve to be used in the gradation conversion process to the target image without considering the observation environment in case of observing the printed material of the target image, the fact that the human's visual characteristic changes according to the observation environment, and the like. Otherwise, the conventional apparatus or system is structured to set the gradation correction curve in the state that the observation environment in case of observing the printed material of the target image, the fact that the human's visual characteristic changes according to the observation environment, and the like can not be considered. In addition, the conventional apparatus or system is structured to set the gradation correction curve to be used in the gradation conversion process for the target image without considering the relation between a gradation range capable of performing image output by the monitor and a gradation range capable of performing image output by the printer.
Therefore, conventionally, when the printed material is observed, there may be a case where it is very difficult for a user to view or observe the printed material according to an environment at this time or a change of the user's visual characteristic.
For example, when a printed material (i.e., a print-output image) is observed in the dark observation environment, the contrast of the image is visually low or visually too dark as compared with the case where the image displayed on the display is observed. On the other hand, when the printed material is observed in the light observation environment, the contrast of the image is visually high or visually too bright as compared with the case where the image displayed on the display is observed.
Moreover, as a structure to set a gradation correction curve which paid attention to the relation between the gradation ranges of two output devices (e.g., a monitor and a printer), for example, there is the structure which is described in Japanese Patent Application No. 2000-263151. This structure is to set the gradation correction curve under the condition of paying attention only to the gradation range, but is not to set the gradation correction curve under the condition of considering an observation environment and a change of the visual characteristic of a viewer. Thus, according to this structure, there is no problem in an ordinary observation environment, but such a problem as above that it is difficult to view the image occurs if the observation environment changes.